Who is Jeff ?

Joshua is my eldest brother's son who is staying in Malacca and has come to visit grandma since Wednesday and will going back this Sunday. He is 5 years old and is english educated hence he don't know how to speak chinese and he is christian. Today di di play with him at my mum's house, both of them seem communicate well in english and have lots of fun playing together. When I'm leaving he come out and shouted :'bye, bye, Jeff....see you again, Jeff !!' Jeff ??? Who is Jeff ? Why he called di di Jeff ?? so I asked him and he said :'dunno, he told me his name is Jeff ....' while pointing at di di.....and when I looked at di di he keep smiling ......kekekkekek.....I never know di di has english name called Jeff ? It is so cute and smart that he named himself Jeff in order to make Joshua comfortable with him...... :D